1. Field of the Invention
The present invention relates to a toothed belt, which may be a so-called timing belt or synchronous belt, used as a power transmission belt in, for example, an engine of a vehicle such as an automobile, to transmit a rotational force of a crank shaft thereof to a cam shaft, a balancer shaft, a drive shaft of a fuel injection pump and so on.
2. Description of the Related Art
Conventionally, such a toothed belt comprises a toothed rubber layer having teeth formed on a surface thereof, a back rubber layer adhered to the other surface of the toothed rubber layer, and a plurality of cord elements embedded in a boundary between the toothed rubber layer and the back rubber layer.
Recently, with the advance in performance of an engine of a vehicle, such as an automobile, the number of revolutions of the an engine has increased. The toothed belt used to rotationally drive a cam shaft, a fuel injection pump or the like is subjected to a larger load.
Breakage of the teeth of the toothed belt is prematurely caused because of the larger stress and strains of an increasing load to which the toothed belt is subjected and, consequently, the service life of the toothed belt is shortened.